The type 2 cannabinoid receptor (CB2R) was initially regarded as a peripheral cannabinoid receptor. However, recent technological advances in gene detection, alongside the availability of transgenic mouse lines, indicate that CB2Rs are expressed in both neurons and glial cells in the brain under physiological and pathological conditions, and are involved in multiple functions at cellular and behavioral levels. Brain CB2Rs are inducible and neuroprotective via up-regulation in response to various insults, but display species differences in gene and receptor structures, CB2R expression, and receptor responses to various CB2R ligands. CB2R transcripts also differ between the brain and spleen. In the brain, CB2A is the major transcript isoform, while CB2A and CB2B transcripts are present at higher levels in the spleen. These new findings regarding brain versus spleen CB2R isoforms may in part explain why early studies failed to detect brain CB2R gene expression. Here, we review evidence supporting the expression and function of brain CB2R from gene and receptor levels to cellular functioning, neural circuitry, and animal behavior.

中文翻译：

---

脑大麻素CB2受体研究进展：从基因到行为。

2型大麻素受体（CB2R）最初被认为是外周大麻素受体。然而，基因检测方面的最新技术进步以及转基因小鼠品系的出现表明，在生理和病理条件下，CB2R 在大脑中的神经元和神经胶质细胞中表达，并参与细胞和行为水平的多种功能。大脑 CB2R 是可诱导的，通过上调来响应各种损伤，从而具有神经保护作用，但在基因和受体结构、CB2R 表达以及受体对各种 CB2R 配体的反应方面表现出物种差异。大脑和脾脏之间的 CB2R 转录本也有所不同。在大脑中，CB2A 是主要的转录亚型，而 CB2A 和 CB2B 转录本在脾脏中含量较高。这些关于大脑与脾脏 CB2R 亚型的新发现可能部分解释了为什么早期研究未能检测到大脑 CB2R 基因表达。在这里，我们回顾了支持大脑 CB2R 表达和功能的证据，从基因和受体水平到细胞功能、神经回路和动物行为。